Interesting excerpts from the CFD rule book.
"Our equipment represents the time period between Samuel Colt’s invention of the Colt .45 Peacemaker in 1873 and 1899, the hey-day of the American Old West. The spirit of our game is that competitors must use six-guns that were commonly used in the late 1800s time frame. See the equipment section for the appropriate firearms that can be used in Cowboy Fast Draw©.
The western holster was also heavily impacted by Hollywood and then much further by the competitive Sport of Fast Draw itself throughout the 20th Century. Historical holster terminology and evolution have been very hard to define, since many experts have conflicting views and interpretations. We have done our best to draw clear lines in order to keep holsters and belts designs as period correct as possible, while not being so strict to limit reasonable interpretations and cosmetic embellishments."
Page 16 shows a drawing of a holster with a skirt and a loop holding the holster to the skirt. And says that on Mexican drop loop holsters you can put the flash deflector between the holster and the skirt.
Again another excerpt from the CFD rule book:
"While there may be some difference of opinions on time frames of certain holsters, we accept the fine book Packing Iron - Gunleather of the Frontier West- by Richard C. Rattenbury as the standard we base our rules upon."
Could not find Reds holster in Packing Iron
It is possible that they are interpeting it to be a variant of the Mexican loop because of the one piec construction folding over to form the belt loop.
Looking in four different books including Packing Iron define Mexican loop as " Formed from a single piece of pattern cut leather, the holster portion ws folded over vertically and sewn along it's main seam to create the body or pouchfor the revolver. The full back panel (typically cut with 2, 4, 6 slitsdepending on length) was folded down horizontally, forming a spacious belt loop and contoured skirt behind the holster body. THe pouch was then passed through or dropped through the the slits, creating one or more integeral loops.That secured the bosy and back skirt as one unit."
In talking to the Curator at the Autery, this is the defenition they use when labeling something as a Mexican loop. They recognize the variants such as the Dodge City, Cheyene, T strap (Jock Strap) etc. as Mexican loop holster because they share they all have the atributes of a Mexican loop which are the one piece holster and skirt construction with loops that hold the holster body to the skirt.
Sorry to be long winded. Again this is the supposed historical defenition of a Mexican Loop holster.